That's "You're already dead." Very very butchered, though.
So many otaku captains here...
"Ore, sanjou!" - When making a Big Damn Heroes' entry screaming out of Full Impulse to save an optional. :p
"Atatatatatata!" - Cannon Rapid Fire
"Hen...shin!" - Transforming the Chimera
That said, I haven't exactly a 'catch phrase'. Things like ordering my coffee/tea from a replicator, straightening my shirt before starting an STF, and having team chat buttons on hot key are more my kind of thing.
If there's something that I say often, its reading off all my tac buff skills as I hit them, ending with Fire On My Mark, then "WAVE MOTION SPINAL LANCE, MARK!"
The 'Minister of Finance' always gives me weird looks when I'm playing STO.